GAD-A219

999

Transionospheric Scintillation and TEC Studies

Michael J. Klein C. Charley Andreasen John M. Lansinger

Northwest Research Associates, Inc. 300 120th Avenue, N.E. Bldg 7, Suite 220 Bellevue, WA 98005

30 December 1988

'n~C Scientific Report No. 19

Approved for public release; distribution unlimited

Geophysics Laboratory Air Force Systems Command United States Air Force Hanscom AFB, MA 01731-5000

"This technical report has been reviewed and is approved for publication"

GREGORY J0 P Contract Ma&_.Branch )

&

W I LIAM K. VICKERY Chief

FOR THE COMMANDER

ROBERT 11-"KRIVANEK Divisiou/irector

This report has been reviewed by the ESD Public Affairs Office (PA) and is releasable to the National Technical Information Service (NTIS). Qualified requestors may obtain additional copies from Defense Technical Information Center. All others should apply to the National Technical Information Service. If your address has changed, or if you wish to be removed from the mailing list, or if the addressee is no longer employed by your organization, pleasenotify GL/IMA Hanscom AFB, MA 01731. This will assist us in maintaining a current mailing list. Do not return copies of this report unless contractual obligations or notice on a specific document requires that it be returned.

Unclassified SECURITY CLASSIFICATION OF THIS PAGE

REPORT DOCUMENTATION PAGE lb. RESTRICTIVE MARKINGS

la. REPORT SECURITY CLASSIFICATiON

Unclassified 3. DISTRIBUTION IAVAILABILITY OF REPORT

2a. SECURITY CLASSIFICATION AUTHORITY

Approved for public release;

Di stri buti on unl imi ted

2b. DECLASSIFICArION /DOWNGRADING SCHEDULE 4. PERFORMING ORGANIZATION REPORT NUMBER(S)

MONITORING ORGANIZATION REPORT NUMBER(S)

.5.

GL-TR-89-0226

NWRA-CR-88-R035 6a. NAME OF PERFORMING ORGANIZATION

Northwest Research Assoc. Inc

7a. NAME OF MONITORING ORGANIZATION

6b. OFFICE SYMBOL (If applicable)

Geophysics Laboratory

CR Division

7b ADDRESS (City, State, and ZIP Code)

6c. ADDRESS (City, State, and ZIP Code)

Hanscom AFB, MA

300 120th Ave. N.E., Bldg. 7, Suite 220 Bellevue, WA 98005 6b. OFFICE SYMBOL

Ba. NAME OF FUNDING/SPONSORING ORGANIZATION

(If applicable)

Geophysics Laboratory

LIS

MA

9. PROCUREMENT INSTRUMENT IDENTIFICATION

F19628-87-C-0003

01731-5000

162101F 11

NUMBER

10. SOURCE OF FUNDING NUMBERS PROJECT TASK PROGRAM ELEMENT NO. NO. NO.

8c. ADDRESS (City, State, and ZIP Code)

Hanscom AFB,

01731-5000

4643

WORK UNIT ACCESSION NO.

AC

10

TITLE (Include Security Classification)

Transionospheric Scintillation and TEC Studies 12. PERSONAL AUTHOR(S)

Michael J. Klein, C. Charley Andreasen, and John M. Lansinger 1 FROM77Z_87

Scientific #19

__

s.

14. DATE OF REPORT (Year, Month, Day)

13b. TIME COVERED

13a. TYPE OF REPORT

TO 9/30/881 December 30,

1988

PAGE COUNT

56

16. SUPPLEMENTARY NOTATION

18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number)

COSATI CODES

17. FIELD

GROUP

SUB-GROUP "-,

Ionospheric effects,'GP 'data acquisition system, data acquisition software,' TA variation; amplitude scintillation

19. ABSTRACT (Continue on reverse if necessary and identify by biock number)

This report describes engineering and technical support involving the operation, maintenance, and enhancement of a GPS data collection

system that is operated at Thule AB, Greenland, and AFGL at Hanscom AFB, MA, for the purpose of studying transionospheric propagation effects. Software upgrades and improvements are described that relate and the and recovery, problem detection to data acquisition, production of 1uick-look4 ata summaries containing TEC and amplitude An analysis made of data collected at scintillation measurements. Thule from October 1987 through March 1988 revealed that a direct relationship was observed between TEC enhancement and scintillation Comparisons are made of fade depth statistics observed activity. during the report period with earlier similar measurements taken , throughout the peak of the last sunspot cycle. 20. DISTRIBUTION/ AVAILABILITY OF ABSTRACT 0] SAME AS RPT. 0-UNCLASSIFIED/UNLIMITED 22a. NAME OF RESPONSIBLE INDIVIDUAL

Gregory Bishop DD FORM 1473, 84 MAR

21. ABSTRACT SECURITY CLASSIFICATION 0"DTIC USERS

Unclassified 22b. TELEPHONE (Include Area Code)

22c. OFFICE SYMBOL

GL/LIS 83 APR edition may be usedunt exhausted. All other editions are obsOlete.

SECURITY CLASSIFICATION OF -HIS PAGE

CONVERSION TABLE Conversion factors for U.S. customary to metric (SI) units of measurement. To convert from

to

Multiply by

angstrom

meters (m)

atmosphere (normal)

kilo pascal (kPa)

1.000000 x 10 + 1.013 25 x I0 2

bar

kilo pascal (kPa)

1.0o0 000 x 10

10

meter (m2)

British thermal unit (thermochemica!)

joule (J)

cal (thermochemical)/ cm

2

2

1.000 000 x 10-28

2

barn

+

+ 1.054 350 x 10 3

mega joule/m

2

2 (Mi/m )

-2

4.184 000 x 10

calorie (thermochemical)

joule (J)

4.184 000 x 10 +3

curi,

giga becquerel (GBq)

3.700 000 x 10 + 1

degree Celsius degree (angle)

degree kelvin (K) radian (rad)

t.= t + 273.15 2 1.745 329 x 10-

degree Fahrenheit

degree kelvin (K)

x

erg

joule (J) joule (J)

erg/second

watt (W)

1.602 19 x 10-19 7 1.00000 x 10-7 1.000 000 x 10

foot

meter (m)

3.048 000 x 10-1

foot-pound-force gallon (U.S. liquid)

joule (J)

1.355 818

electron volt

- (t*F + 459.67)/1.8

3

Gauss

Tesla

3 3.785 412 x 104 1.000 000 x 10

inch

meter (m)

2.540 000 x 10-2

joule/kilogram (J/kg) (radiation dose absorbed)

gray (Gy)

1.000 000

kilotons

terajoules newton (N)

4.183 +3 4.448 222 x 10 6.894 757 x 10 + 3

kip (1000 1bf) 2 kip/inch (ksi)

meter3 (m )

kilo pascal (kPa) 2 2 newton-second/m (N-s/m )

ktap

+ 1.000 00 x 10 2 6

micron

meter (m)

1.000 000 x 10-

mi

meter (m)

mile (international)

meter (m)

2.540 000 x 101.609 344 x 10 + 3

ounce

kilogram (kg)

2.834 952 x 10.2

pound-force (1bf avoirdupois) pound-force inch

newton (N) newton-meter (N-m) newton/meter (N/m)

4.448 222 1.129 848 x10-1 1.751 268 x 10 + 2

kilo pascal (kPa)

4.788 026 x 10-2

2 pound-force/inch (psi) pound-mass (Ibm avoirdupois) 2 pound-mass-foot (moment of inertia)

kilo pascal (kPa)

6.894 757

kilogram (kg) 2 2 kilogram-meter (kg-m )

4.535 924 x 10-1 4.214 011 x 10-2

rad (radiation dose absorbed)

gray (Gy)

roentgen

coulomb/kilogram (C/kg 1

1.000 000 x 10-2 4 2.579 760 x 10-

shake

second ts

slug

kilogram (kg)

1.000 x 10-8 + 1.459 390 x10 1

tort (mm Hg, 0,C)

kilo pascal (kPa)

1.333 22 x 10-1

5

pound-force/inch pound-force/foot

2

iii

TABLE OF CONTENTS Page 1.

Introduction

1

2.

Objectives

1

3.

Operation and Maintenance of GPS Monitoring Equipment

2

4.

Software Upgrades and Enhancements

3

5.

4.1

Data Acquisition Software

3

4.2

Improvements to the Real-Time Routine

3

4.3

Problem Detection and Recovery

4

4.4

Primary Analysis Routine

4

4.5

Quick-Look Summaries

5 5

Production ?Y P INSF CIED

6.

Final Data Analysis Aecession For NTIS

C A&I

DTIC TAB

Ju:;t Iflc: tlon

Ji, 1

-"

0'

7

LIST OF FIGURES Figure

Caption

1

Percent occurrence of various fade levels with active TEC observations, from Thule, Greenland, October 1987 through March 1988.

2

Percent occurrence of various intensity fade levels within all TEC observations, from Thule, Greenland, October 1987 through March 1988.

3

Monthly summaries over the study period showing occurrence of TEC, Scintillation Activity, and foF2 as a function of universal time.

4

Measurements from GPS and polar beacon satellite passing within 1 degree show TEC variations linked to strong amplitude scintillations at 250 MHz.

5

Occurrence of 15-minute fade depth indices from 1979 through 1984. LIST OF APPENDICES

Appendix

Description

A

Twelve representative examples of equivalent slant covering period day 290, 1987, through day 88, 1988.

B

Description of the standard AFGL procedure to measure fade depth.

C

Database utilized in final data analysis.

D

Curves of the probability of a period without an event for all active data given several methods of categorizing the data.

vi

TEC

1.

Introduction

This report describes work performed by Northwest Research Associates on contract with the Air Force Geophysics Laboratory (AFGL), Ionospheric Effects Branch (LIS), to provide hardware and software support enabling the presentation of a special scaled data set characterizing ionospheric effects at Thule, Greenland. Hardware support consisted of the responsibility of insuring operation and maintenance of the monitoring equipment; repair of associated equipment including computers, tape drives, receivers and other components; implementation of system upgrades; and installation of additional systems. Software support of the TRN objective included installing and customizing operating system upgrades, installing and learning new vendor software to assist others on the team, writing utilities and software tools, and upgrading existing routines. Additional activities included the organization and cataloging of tapes and charts coming from the study site and acquisition of necessary materials required for the study. The study consisted of a five step process: (1) Collecting five channels of raw data determined from signals received from GPS system satellites onto tape and chart records. (2)

Cataloging

these

items

as

they were

received

at

the

AFGL. (3) Identifying elements of the data for potential analytical significance to the study. (4) Converting analysis.

the

raw

data

and

performing

first-phase

(5) Performing final analysis on data passing the first phase. The results of this process were plotted and provided to the sponsor, as required by the TRN. 2.

Objectives

The objectives of this TRN were to provide engineering and technical support for the enhancement and operation of groundbased satellite monitoring equipment that provide data important in the evaluation of ionospheric effects on transionospheric RF systems.

These entailed:

3.

a.

Development and enhancement of the GPS data acquisition system at Thule AB, Greenland, and AFGL at Hanscom AFB, Massachusetts.

b.

Installation, maintenance, and operation of the aforementioned systems.

c.

Organization, categorization, and analysis of the various information measures obtained from these systems.

d.

Improvement and development of new systems which facilitate analysis and which will accommodate various resources available at AFGL (such as: DEC pdp 11/03's, DEC Micro pdp 11, DEC VAX, CDC Cyber, and various PC systems).

e.

Utilization of existing systems and enhancment and creation of new analysis systems to develop parameter statistics and plots.

Operation and Maintenance of GPS Monitoring Equipment

One of the key elements in the GPS monitor system, and a primary focus of attention, is the GPS satellite receiver. Installation, calibration, repair, and maintenance of the receiver systems at Thule require one- to two-week trips every two to three months. Often it is necessary to ship equipment back to the laboratory at AFGL for repair. Other situations are dealt with by phone, analyzing the problems and instructing the Danish technicians how to proceed. In November, 1987, an on-site receiver evaluation at Thule revealed thp necessity of replacing a receiver component for which there was no readily available spare. While there, a new receiver arrived at AFGL, prompting the decision to curtail the trip, bench-check the new receiver at AFGL, and obtain the necessary replacement component. Another trip to Thule was made to install the new receiver and repair and retain the old receiver cn site as a backup. In early 1988 a decision was made to expand observation at Thule. A second system was assembled from spare parts which would allow observation of high-elevation satellites on the current system and concurrent observation of low-elevation satellites on the newly assembled system. In early June the new system was installed, and upgraded acquisition software was installed on both systems at that time. The GPS development system at AFGL was deployed to Kwajalein Island in the South Pacific in late July, 1988, to participate in 2

the DNA-sponsored Propagation Effects Assessment-Kwajalein (PEAK) campaign. NWRA personnel installed and operated the system for The system was subsequently the six-week duration under TRN #13. shipped to Thule to participate in another campaign to be conducted in December, 1988, and to serve as a complete backup for the two systems on-site. 4.

Software Upgrades and Enhancements

A preparatory effort was undertaken at the outset of the TRN to implement refinements and anticipate potential problems. This entailed upgrading and enhancing the software portions of the GPS collection and analysis systems, and correcting and improving the Additionally, hardware portions of the GPS acquisition system. software tools were created to extend ability to deal with known data requirements. 4.1

Data Acquisition Software

The data acquisition system software, which operates on the The satellite DEC pdp 11/03's, was analyzed and upgraded. 'window' portions were streamlined, and enhancements were devised to:

4.2

a.

Improve satellite 'window' information entry, deletion, and revision.

b.

Provide for automatic update of satellite 'window' elements that previously had become gradually obsolete over a few weeks. This eliminated a cause for frequent attention to satellite 'window' elements.

c.

Offer a choice of Danish instructions as an alternative to English to reduce the possibility of misunderstanding by the technicians who perform day-to-day operations. The translations were performed by NWRA's Mr. C. Charley Andreasen.

Improvements to the Real-Time Routine a.

The real-time routine that acquires data was streamlined as well. The following corrections were made: (1)

Solving an intermittent failure to detect the end of a satellite pass, which caused the system to lose useful data over the succeeding 24 hours.

(2)

Performing a check to prevent an operator from erroneously instructing the system immediately to start taking data from a satellite that is not available at that time.

3

(3)

b.

4.3

Allowing the system to detect the loss of 'lock' by the receiver on the current satellite, thereby halting acquisition of invalid data.

Enhancements to the real-time routine included: (1)

Creation of a Danish language version of the acquisition routine, automatically invoked according to the choice made in the 'window' routines (Separate English and Danish version of this routine were necessary due to its size and hardware restrictions).

(2)

the Implementation of a header that records satellite (space vehicle) number, Julian date and year of the pass, and the session operator. satellite number and Julian (Previously, the date/year were determined and added manually during the analysis phase.) Automation eliminated the potential for error and reduced manpower requirements. Recording the session operator provided a means for tracking operator errors.

Problem Detection and Recovery

Software tools were created to facilitate problem detection and recovery, which included: a.

A routine to allow a quick look at raw data, averaged to six-second quantities (data are collected at 20 values per second in binary format), enabling trace-back of faults noted.

b.

A routine to select valid data from a satellite pass file that failed to end appropriately and save it in a separate file.

c.

A program to copy selected files to a separate tape to enable analysis of only those files.

4.4

Primary Analysis Routine

Refinements were made to the primary analysis routine, which converts the raw GPS measurements into slant Total Electron Content (TEC) values, enhancing functionality. Access to the header information, now recorded in the acquisition system, was added. Multipath correction of Differential Group Delay procedures, Other enhancements were developed under TRN #13, was added. attempted, but architectural/system constraints of the CDC Cyber, the primary analysis system, prevented their implementation. Alternative solutions are under consideration.

4

4.5

Quick-Look Summaries

Procedures were established for the generation of 'quicklook' data summaries. An dctivity quantifier measure (see the Table on page 6) was established whereby hourly activity levels in GPS TEC measurements and polar beacon satellite 250-MHz A visual amplitude scintillation measurements were tabulated. examination of chart records from Thule would be performed as they arrived and a tabulation made accoraing to the standard developed. This enabled analysis to be focused on pass files with significant ionospheric activity. 5.

Production

Production work and preparatory work were performed concurrently in the early stages of the TRN. Production work consisted of reviewing the tapes and charts arriving from Thule, cataloging them, visually examining the chart records, and tabulating the Using activity levels according to the criteria described above. criteria outlined in the Table, active periods of significant TEC gradients or significant fades from 250-MHz beacon satellite meaRaw data occurring during these surements were identified. active periods were then processed by the first level of GPS analysis, which converted GPS differential carrier phase measurements to slant TEC variation. Differential carrier phase measurements were considered the best available measure to indicate the rapidity of change in the ionosphere. Absolute TEC measurements, available from a measure of differential group delay output from the GPS receiver, are less suitable for this study because of susceptibility to system noise and multi-path effects. 'event' analyzer was To perform the final analysis, an developed. This enabled large quantities of 'significant' activity to be efficiently analyzed and quantified according to activity level. Several approaches were examined and tested for characterizIt ing TEC measurements specific to a particular satellite pass. was decided to assess the TEC data by determining a measure of The the TEC gradient over a sliding 360-second sampling period. measured 'event' gradient was determined by the difference of the means of five samples at 40-second intervals in the first half An 'event' level of and the second half of the sampling period. 6 electrons/m 2 'I' was defined as a measured difference of 3.3xi0 occurring in the 40-second time difference interval. A routine was developed to tabulate slant TEC measurements, 'event' magnitude, and satellite azimuth and elevation over the duration of the pass. These routines were further upgraded to determine the probability of an event occurrence and the probability of no event during a period twice the defined 'event' length and display the results. Twelve representative samples of

5

Table i. Activity quantifier for GPS and 250 MHz beacon data.

GPS

250 MHz Beacon

Comment

Quiet

I

A>0.5 TEC u/10 min

Small

2

A